Mike Bloomberg began the year as a billionaire businessman with no political experience – and he’ll end it holding the record for the most expensive self-financed city campaign in history.

He was best known by the political press for his on-the-trail gaffes, his off-the-cuff comments – and his flashes of temper in the final weeks.

But what most voters saw were his ads and the glossy mailings touting Bloomberg as the second coming of Rudy Giuliani.

And while he got a reputation for being an undisciplined candidate for most of the six months he spent on the stump, most of the mistakes that pundits thought would be fatal to Bloomberg’s campaign were all but forgotten after the Sept. 11 terror attacks.

The price tag for Bloomberg’s first run for public office is expected to be well over $50 million – the most ever spent on a local race in the country.

Whatever his final spending bill turns out to be, Bloomberg – the lifelong Democrat who jumped to the Republican ,CBParty last year – has already poured out more money than either Hillary Rodham Clinton or Rick Lazio spent on their Senate campaigns last year.

Bloomberg’s deep pockets were both a plus and minus for him, early voter exit polls showed yesterday.

While Bloomberg troubled about half the voters in the poll with his high spending, he never would have driven the general election to a dead heat without it.

The Edison Media Research exit survey showed 24 percent of people were “very concerned” about the money Bloomberg pumped into his campaign on ads, mailings, phone-bank calls and high-priced consultants.

Another 18 percent said they were “somewhat concerned.”

But 22 percent said they were “not too concerned” about Bloomberg’s millions, while 37 percent said it didn’t bother them at all.

The bulk of Bloomberg’s spending spree went to advertisements – with six different pricey TV spots running at one point late in the race.